Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This is increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease.
Diabetes has been shown to cause certain problems. For example, people with diabetes can get high blood pressure, kidney disease, nerve damage, heart disease, and even in certain circumstances blindness. The damage caused by these problems may occur in patients whose blood sugar has been out of control for years. Keeping blood sugar under control, by way of effective insulin administration, is one method that can help prevent this damage from occurring.
In addition, people with diabetes can go into “diabetic coma” if their blood sugar is too high. They can also develop blood sugar that is too low (i.e, hypoglycemia) if they don't get enough food, or they exercise too much without adjusting insulin or food. Both diabetic coma and hypoglycemia can be very serious, and even fatal, if not treated quickly. Closely watching blood sugar, being aware of the early signs and symptoms of blood sugar that is too high or too low, and treating those conditions early can prevent these problems from becoming too serious.
Pen type drug delivery devices have been designed and developed to help patients suffering from diabetes so as to prevent such problems from occurring. The circumstances identified above highlight a number of design considerations and criteria for drug delivery devices, especially those that may be used to treat diabetes. As just one example, one requirement is that the drug delivery device must be robust in construction. The drug delivery device must also be easy to use both in terms of the drug delivery device manipulation and understanding of the device's operation. Diabetics have to inject themselves repeatedly with insulin solution and the volume of insulin to be injected may vary from patient to patient and even from injection to injection. For at least this reason, certain diabetics may require drug delivery devices that allow the patient to inject successive measured dosages of the same or perhaps different preset volumes of insulin solution accurately and with minimum dexterity challenges. This presents a further design challenge since, in the case of certain diabetics, users may have impaired vision and/or may be physically infirm with limited dexterity.
Pen-type injectors are well known and typically each use some form of a piston rod to axially drive or push a rubber stopper in a cartridge towards the distal end of the injector to dispense medicament from the cartridge through an attached needle. Such injectors have application where regular injection by persons without formal medical training occurs. This is increasingly common amongst those having diabetes where self-treatment enables such persons to conduct effective management of their diabetes.
These circumstances set a number of requirements for pen-type injectors of this kind. The injector must be robust in construction, yet easy to use both in terms of the manipulation of the parts and understanding by a user of its operation. In the case of those with diabetes, many users will be physically infirm and may also have impaired vision. Where the injector is to be disposable rather than reusable, the injector should be inexpensive to manufacture and easy to dispose of (preferably being suitable for recycling).
One problem frequently encountered when using these pen-type is high dispensing loads that can be caused by a blocked or clogged needle, or where the user forgets to attach a needle, or where the user applies excessive force during the injection, typically by injecting too fast. A drive member or sleeve ultimately transmits these high dispensing loads to the proximal end of the piston rod, which in turn transmits the forces to the piston or bung in a cartridge of medicament. Such loads manifest themselves as rotational and/or axial forces and can cause jamming of the device and even shearing or breaking of the piston rod.